PURPOSE: To set the delay time which is set in the change of the air-fuel ratio from rich side to lean side in order to prevent the misfire in the state where the measurement of the intake air quantity becomes inmcorrect because of the change of the operation state, to the optimum length for a variety of engines so that the fuel consumption is improved and the traveling performance is secured.
CONSTITUTION: A delay time Ts is set in the change from the rich state to the lean state of the air-fuel ratio in the transition from acceleration to stationary state of the engine operation state. A timer Tu is set immediately after the change of a stoichi flag for instructing of the rich control after the lapse of the delay time Ts (S302), and it is detected if misfire is generated during the operation of the timer Tu (S303), and if misfire is generated, the delay time Ts is set longer (S304), while if no misfire is generated, the delay time Ts is shortened (S305). Accordingly, the delay time Ts is corrected so that the lean region can be made as wide as possible, preventing the deterioration of the traveling performance due to the misfire.
SUGA TOSHIYA
SAKAMOTO KATSUHIKO
